Torque converters generally utilize three major rotating elements, namely a pump impeller (a driving member), a turbine runner (a driven member), and a stator located at the inner portion of the converter between the pump impeller and the turbine runner. The three major rotating elements cooperate with each other to provide oil circulation passage within the converter unit. Concretely, during operation of the driving power source (engine), the pump impeller is driven by input torque from the power source. When the engine is running and thus the pump impeller is rotating, the working fluid or working oil is pumped from the impeller blades across to the turbine blades, then back to the pump impeller via the stator for torque transmission from the impeller to the turbine.